This invention relates to labels. More particularly, this invention relates to secure, machine readable labels that are conducive to the detection of bar-codes and other types of markings, or indicia, that have varying spectral emissivity values.
Various marking techniques have been used for identification and authentication purposes. For example, machine-readable codes (e.g., bar-codes) and other types of indicia have been used to attach important information to documents and other types of products such as clothing, accessories and the like. The information provided by these machine-readable codes has typically included the origin, authorship, history, ownership and/or other features of the product to which the code is attached. In the case of envelopes or packages to be mailed, for example, bar-codes have been used to provide evidence of proper postage paid. Meanwhile, for example, pricing information has been embedded in bar-codes used in the case of retail product labeling.
As protection against counterfeiting has become an increased concern, moreover, the use of various types of “invisible” marking techniques has became much more prevalent. For example, indicia that uses ultraviolet (UV) and infrared (IR) inks have become widely used. One benefit of using these types of inks is that they are typically not visible when illuminated with light in the visible spectrum (i.e., about 400-700 nm), but are visible when illuminated with light in the UV spectrum and IR spectrum, respectively. Thus, as with the other types of “invisible” indicia, an individual is unable to tell whether the product contains a security mark by merely looking at the product with the naked eye. Similarly, magnetic materials which are detected through their perturbation of a magnetic field have also been used.
Despite the early success of the above-described types of indicia, they have become more vulnerable to copying, alterations and counterfeiting as a result of technological advancements. For example, indicia using UV ink are easily detected through the interaction of the ink with radiation. In addition to mere detection, moreover, indicia using UV inks have proven to be susceptible to copying, alterations and counterfeiting (e.g., through the use of conventional office products).
An alternate type of indicium that is more related to the present invention is disclosed in commonly owned, co-pending U.S. patent application Ser. No. 10/355,670, filed Feb. 1, 2003, entitled “Information Encoding On Surfaces By Varying Spectral Emissivity,” which is hereby incorporated by reference in its entirety. This type of indicium is implemented by modifying a surface such that it has varying emissivity values, where emissivity is the ability of the given surface to emit radiant energy compared to that of a black body at the same temperature and with the same area. For example, at least two patterns that differ in spectral emissivity by known amounts are used to form a machine-readable code or other type of marking-that can be detected (and/or decoded) through the use of a scanner (e.g., a laser spot scanner or an active laser pyrometer) that is capable of detecting emissivity differentials. In general, these patterns are preferably indistinguishable from their surroundings. Moreover, even when visible, the emissivity values of the patterns are not subject to duplication by standard office equipment. As such, they are less susceptible to counterfeiting, and can be used more reliably for identification and authentication purposes.
Current labels that may receive bar-codes or other types of markings (e.g., those types of markings described in U.S. patent application Ser. No. 10/355,670), however, are often not adequate. For example, the color and the patterns of the inks used in making a marking are often visible to the naked eye when applied to current labels. As such, it becomes extremely difficult to provide a document or other product with a hidden security marking.
Additionally, current labels are not designed to enable fast, accurate and cheap detection of transitions of differential emissivity for a marking that uses varying spectral emissivity values. For example, the presence of temperature variations along the surface of existing labels often makes the use of more expensive and time consuming scanning equipment necessary given that, in this case, measuring levels of radiated thermal energy alone may not be sufficient to obtain accurate measurements of emissivity values. Additionally, such temperature variations also increase the likelihood that the detection of transitions of differential emissivity will be subject to errors.
In view of the foregoing, it is an object of this invention to provide a machine readable label for receiving indicia having variable spectral emissivity values that alleviate the above and other problems associated with existing labels.